(i) Field of the Invention:
The present invention relates to a method for growing a single crystal, and more particularly to a method for growing the single crystal of an insulator in a defined shape.
(ii) Brief Description of the Prior Art:
As one method of producing a single crystal, there has heretofore been known the floating zone technique wherein a feed rod is heated into a molten zone by radio frequency heating, laser heating, electron beam heating, arc image heating with an ellipsoidal mirror, or the like, and the molten zone is transferred, thereby turning the feed rod into a single crystal. In addition, as a modification of the floating zone technique, there has also been utilized a method wherein a feed rod which is molten is in contact with one surface of a metal plate heater which is heated by causing current to flow therethrough. The melt is guided to the other surface of the metal plate heater through apertures provided in the metal plate heater and is crystallized when contact is made with a seed crystal located on the other surface. By moving the feed rod so as to supply the raw material, the seed crystal is slowly transferred in the direction opposite to the metal plate heater or downwards, thereby growing the single crystal (hereinafter, this method shall be referred to as "modified floating zone technique"). An example of the metal plate heater for use in the modified floating zone technique is shown in FIG. 1. The details of FIG. 1 will be described later.
Among these floating zone techniques, the method resorting to heating with a laser, an electron beam or an arc image find it difficult to prepare crystals of large diameter because the power of the heat source is low. On the other hand, in the case of employing the radio frequency heating method, it is possible to obtain a sufficiently high power and thus to grow a crystal of large diameter. However, the raw material must be a conductor.
In contrast, due to the use of the resistance-heated metal plate heater, the modified floating zone technique can grow the single crystal even when the raw material is an insulator. In addition, the crystal of large diameter is obtained. With the modified floating zone technique, however, the melt spreads over the entire area of the metal plate and it arrives even to a lead portion for power supply in the worst case, which makes it difficult to stably hold the molten zone. Accordingly, a single-crystal having a uniform diameter cannot be grown by the modified floating zone technique. This has been the serious difficulty of the modified floating zone technique.